In recent years, liquid crystal display devices have come to be widely used in smartphones, personal digital assistants (PDAs), tablet computers, satellite navigation systems, etc. In general, a liquid crystal display device comprises a liquid crystal display panel and a surface illumination device (backlight device) which is overlaid on the rear surface of the liquid crystal display panel and illuminates the liquid crystal display panel. An example of the surface illumination device is a backlight unit including a reflective layer, a lightguide plate (lightguide), an optical sheet, LEDs as light sources, and a rectangular mold frame. The reflective layer, the lightguide plate, and the optical sheet are stacked on each other, and disposed in the mold frame. The peripheries of the reflective layer, the lightguide plate, and the optical sheet are thereby supported and positioned by the mold frame.
In recent years, as display areas have increased, there has been a continual demand for the frames of liquid crystal display devices to become ever narrower and the liquid crystal display devices to become ever thinner. However, the dimensions of the width, thickness, etc., of the mold frame in the above-described backlight unit is approaching the structural limit of injection molding.